By: Deborah FallowsRepublished by Atlantic. View the article at the Atlantic website here.

"You can only do one thing at a time: talk to the baby or talk on the phone."

Last summer, as my baby grandson and I strolled through the same neighborhood his father and I had strolled through 30 years earlier, I saw that something vital had changed. Back then, adults pushing babies in strollers talked with those babies about whatever came across their path. But these days, most adults engage instead in one-sided conversations on their cellphones, or else text in complete silence.

As a linguist, I wondered whether the time adults spend with their mobile devices might be affecting the way children learn language. Since the technology hasn’t been ubiquitous for long, research on this question is scarce. But other research on the effects of adult-child conversation makes a strong case for putting cellphones away when you’re around children.

For a study published in the journal Pediatrics in 2009, researchers outfitted young children with small digital recorders, which captured the language each child heard and produced. The researchers could then identify and count the two-sided exchanges, or conversational “turns,” between children and adults. Subjects were also tested on a range of linguistic measures, from the earliest preverbal behaviors, to nascent phonology and grammar skills, to preliteracy and the integration of complex parts of language.

The children exposed to more conversational give-and-take scored higher at every stage of language proficiency. In essence, the children made greater linguistic strides when adults talked with them than when they were simply in the presence of language or even when adults talked to them. We learned long ago that children’s language abilities and eventual academic success are linked to the sheer volume of words they are exposed to early on. Now we have additional evidence that the quality of linguistic exposure, not just its quantity, matters.

Two other studies, reported in the Proceedings of the National Academy of Sciencesin 2003, looked at the effects of parent-child interactions on very early stages of language production and perception. In one, babbling infants and their mothers were tracked during on-the-floor playtime. Mothers in one group were directed to respond to their babies’ vocalizations with smiles and touches, and by moving closer. Mothers in the other group were not cued to respond in the same way. The study found that babies whose moms interacted with them in sync with their babbling soon began to vocalize more, with more complex sounds, and articulated more accurately than the other children.

In the other study, 9-month-old babies, who are in the late stages of locking in to the sound system of their native language, were exposed to mini lessons in Mandarin, to see if they could still learn to discern the sounds of a foreign language. One group of babies was taught by real live Chinese speakers. Another group got lessons from electronic versions of the adults, who appeared either on TV or on audiotape. Infants with live teachers learned to discern the sounds of Mandarin, while those in the group with electronic instruction did not.

These studies suggest that social interaction is important to early language learning. Of course, everyone learns to talk. But how ironic is it that, in this era when child-rearing is the focus of unprecedented imagination, invention, sophistication, and expense, something as simple and pleasurable as conversing with our children can be overlooked? As Dimitri Christakis, one of the authors of the Pediatrics paper, put it to me, “You can only do one thing at a time: talk to the baby or talk on the phone.”